Printers for printing out the outputs of computers are understandably varied in configuration. One very popular group, exemplified by NEC Models 2000/3500/8000, is of the daisy wheel type, printing a whole character with each stroke of printer operation. These printers employ a ribbon cartridge wherein a ribbon wound on and between two spools is impacted by a character print element of the printer. Cartridge configurations for these printers are illustrated by Meintrup et al U.S. Pat. No. 4,496,255, Shapiro U.S. Pat. No. 4,533,266 and Kano U.S. Pat. No. 4,544,291. A principal characteristic of such cartridges is that they employ two laterally spaced capstan drives, alternately driven through opposite sides of the cartridge by a rotary drive member of a host printer. One of the capstan drives drives a ribbon in one direction, wherein a top region of the ribbon is utilized in printing, and the other capstan drive drives the ribbon in the opposite direction and a bottom region of the ribbon is utilized. Each of the capstan drives consists of a drive roller and a pinch roller, and each capstan drive is associated with one of two spools of the cartridge. A belt is coupled between the driven roller and its associated spool, driving this spool, as a take-up spool, in a direction to receive the ribbon. This belt is positioned on the outside of the cartridge, connecting between pulleys on shafts of the drive roller and spool. In order to switch directions of drive, the cartridge is turned over and the belt is removed from pulleys on one side of the cartridge and placed around pulleys on the opposite side.
The belt and pulley arrangement discussed is an obvious disadvantage, both from the point of view of inconvenience and the variable tension effected upon the take-up spool as the amount of ribbon on it changes. Perhaps in recognition of the most blatant of these, the inconvenience, Meintrup suggests that an internal belt might be employed and cites a data tape cartridge manufactured by the 3M Company as providing such. This cartridge or cassette is illustrated in Von Behren U.S. Pat. No. 3,692,255, and a ribbon cartridge counterpart of it is illustrated in Sasaki U.S. Pat. No. 4,528,572. Upon examination of these references, it appears that both employ a single, centrally positioned drive member and thus are employable only with drive units, tape drives or printer drives, adapted to interface with a central position on a cartridge and not one where separate, spaced capstan drives are employed as required by the printers referred to above. Clearly, neither of these patents provide a teaching as to how one would employ an internal belt in a ribbon cartridge where the drive positions are spaced apart as in the class of cartridge we are concerned with here. In contrast, the inapplicability is manifest and is obvious from the fact that if a belt were stretched between the capstan drives of Meintrup, with an idler symmetrically positioned, e.g., where the drive roller is positioned in the case of Sasaki, the ribbon would be driven by the belt in one direction and the ribbon spool in an opposite direction, an inoperative condition.
In addition to the belt problem, another problem is that of generally providing needed tension on the ribbon of a dual capstan system. Ribbon tension is particularly necessary in the region where the print elements of the printer impact the ribbon to make an imprint on paper. It is important that the ribbon be held taut and constantly so. If there is insufficient tension, the ribbon will tend to drag on the paper and smudge it. If the tension becomes too great, there is a danger of breakage of a ribbon as a printing element impacts on it. Currently available cartridges constructed in accordance with the prior art simply reply upon mechanicam drag brought about by the frictional state of the bearing surfaces of a pinch roller, a drive roller, and a spool to provide proper tension. Unfortunately, these frictional factors vary, this variance being particularly commercially affected by constantly varying spool sizes as ribbon is fed to and drawn off of the spools. In any event, there is a substantial lack of consistency of ribbon tension.
A still further matter of concern with respect to the merit of ribbon cartridges is that of rate of use of ribbon. Ideally, the ink in the vicinity of an impact by a printing element will be completely utilized but not to the extent that a portion of a character being printed will receive insufficient ink. Pertinently, the rate of ribbon usage is a function of the speed of the rotating drive of the printer and the translation of this speed to a final ribbon drive speed, the latter being a function of the drive mechanism of the cartridge. Since the drive speed is thus fixed by a printer manufacturer, it is up to the ribbon cartridge manufacturer to provide a cartridge which will provide an optimum rate of ribbon advancement for the drive speed at hand. Unfortunately, it appears that because of certain structural limitations imposed by the mechanisms employed in prior art ribbon cartridges, they effect a higher rate of ribbon travel than is actually necessary to provide good print quality. Specifically, it appears that this is the result of employing a direct capstan drive of ribbon, which in turn has necessitated the employment of toothed surfaces to obtain sufficient grip on a ribbon to reliably advance it. This in turn has resulted in an excessive effective diameter of the drive roller, resulting in an excessive effective rate of ribbon advancement.